Laser apparatus, laser annealing method, and manufacturing method of a semiconductor device

ABSTRACT

To provide a laser apparatus and a laser annealing method with which a crystalline semiconductor film with a larger crystal grain size is obtained and which are low in their running cost. A solid state laser easy to maintenance and high in durability is used as a laser, and laser light emitted therefrom is linearized to increase the throughput and to reduce the production cost as a whole. Further, both the front side and the back side of an amorphous semiconductor film is irradiated with such laser light to obtain the crystalline semiconductor film with a larger crystal grain size.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of annealing asemiconductor film with the use of laser light (hereinafter referred toas laser annealing) and to a laser apparatus for performing the laserannealing (an apparatus including a laser and an optical system forleading laser light output from the laser to a process object). Theinvention also relates to a semiconductor device fabricated by amanufacturing process that comprises the laser annealing step, and tothe manufacturing process. The semiconductor device here includes anelectro-optical device such as a liquid crystal display device and an ELdisplay device, and an electronic device having the electro-opticaldevice as one of its components.

[0003] 2. Description of the Related Art

[0004] An advance has been made in recent years in development of thinfilm transistors (hereinafter referred to as TFTs), and TFTs usingpolycrystalline silicon films (polysilicon films) as crystallinesemiconductor films are receiving the attention. In liquid crystaldisplay devices (liquid crystal displays) and EL (electroluminescence)display devices (EL displays), in particular, such TFTs are used aselements for switching pixels and elements for forming driver circuitsto control the pixels.

[0005] General means for obtaining a polysilicon film is a technique inwhich an amorphous silicon film is crystallized into a polysilicon film.A method in which an amorphous silicon film is crystallized with the useof laser light has lately become the one that is especially notable. Inthis specification, to crystallize an amorphous semiconductor film withlaser light to obtain a crystalline semiconductor film is called lasercrystallization.

[0006] The laser crystallization is capable of instantaneous heating ofsemiconductor film, and hence is an effective technique as measures forannealing a semiconductor film formed on a low heat resistant substratesuch as a glass substrate or a plastic substrate. In addition, the laserannealing makes the throughput definitely higher as compared withconventional heating measures using an electric furnace (hereinafterreferred to as furnace annealing).

[0007] There are various kinds of laser light, of which the general oneto be used in laser crystallization is laser light generated and emittedfrom a pulse oscillation type excimer laser as a source (hereinafterreferred to as excimer laser light). The excimer laser has advantages inthat it is large in output and that it is capable of repetitiveirradiation at a high frequency and, moreover, excimer laser light isadvantageous in terms of its high absorption coefficient with respect tosilicon films.

[0008] To generate excimer laser light, KrF (wavelength, 248 nm) or XeCl(wavelength, 308 nm) is used as an excitation gas. However, Kr (krypton)gas and Xe (xenon) gas are very expensive, causing a problem of increasein production cost when recharge of the gas is frequent.

[0009] In addition, every two or three years, excimer laser annealingrequires replacement of attachments such as a laser tube for laseroscillation and a gas refinery for removing unnecessary compounds thatare produced during the course of oscillation. Many of these attachmentsare also expensive, taking part in increasing the production cost.

[0010] As seen in the above, a laser apparatus using excimer laser lightdoes possess high ability but also possess drawbacks in that maintenancethereof is very troublesome and that the running cost (which means thecosts required for operating the apparatus) is high for a laserapparatus for mass production.

SUMMARY OF THE INVENTION

[0011] The present invention has been made in view of the above, and anobject of the present invention is therefore to provide a laserapparatus which is capable of providing a crystalline semiconductor filmwith a larger crystal grain size than in prior art and which is low inrunning cost, and to provide a laser annealing method using that laserapparatus. Another aspect of the present invention is to provide asemiconductor device fabricated by using the laser annealing method anda method of manufacturing the semiconductor device.

[0012] The present invention is characterized in that the front side andthe back side of a semiconductor film are irradiated with laser lightgenerated and emitted from a solid state laser (a laser that outputslaser light using a crystal rod as a resonance cavity) as a source.

[0013] When the semiconductor film is irradiated, the laser light ispreferably linearized by an optical system. To linearize laser lightindicates that laser is formed into such a shape as to make theirradiated area linear when a process object is irradiated with thelaser light. In short, it indicates that the sectional shape of thelaser light is linearized. The term “linear” here does not mean a linein the strict sense of the word, but means a rectangle (or an oblong)with a large aspect ratio. For instance, a rectangle or an oblong havingan aspect ratio of 10 or more (preferably 100 to 10000).

[0014] In the above construction, the solid state laser may be generallyknown ones such as a YAG laser (which usually indicates an Nd:YAGlaser), an Nd:YVO₄ laser, an Nd:YAIO₃ laser, a ruby laser, a Ti:sapphirelaser, or a glass laser. The YAG laser is particularly preferablebecause of its superiority in coherence and pulse energy. There are acontinuous wave YAG laser and a pulse oscillation type YAG laser and thelatter is desirable in the present invention, for it is capable of largearea irradiation.

[0015] However, the fundamental wave (a first harmonic) of the YAG laserhas as high wavelength as 1064 nm. It is therefore preferable to usesecond harmonic (wavelength, 532 nm), third harmonic (wavelength, 355nm), or fourth harmonic (wavelength, 266 nm).

[0016] In particular, the second harmonic of the YAG laser has afrequency of 532 nm and is within a wavelength range (around 530 nm) inwhich reflection at an amorphous silicon film is the least when theamorphous silicon film is irradiated with the second YAG laser wave. Inthis wavelength range, in addition, the quantity of transmittable laserlight through the amorphous semiconductor film is enough to efficientlyirradiate again the amorphous semiconductor film from its back sideusing a reflective member. Moreover, the laser energy of the secondharmonic is large, about 1.5 J/pulse at a maximum (in an existing pulseoscillation type YAG laser apparatus). When it is linearized, the lengththereof in the longitudinal direction is therefore markedly lengthenedto make it possible to irradiate a large area at once with laser light.These harmonics can be obtained by using a non-linear crystal.

[0017] The fundamental wave can be modulated into the second harmonicthe third harmonic, or the fourth harmonic by a wavelength modulatorthat includes a non-linear element. The respective harmonics may beformed by following any known technique. In this specification, “laserlight generated and emitted from a solid state laser as a source”includes not only the fundamental wave but also the second harmonic, thethird harmonic, and the fourth harmonic which are obtained by modulatingthe wavelength of the fundamental wave.

[0018] Alternatively, the Q switch method (Q modulation switch method)that is often used in the YAG laser may be employed. This method is tosufficiently lower the Q value of a laser resonator in advance and tothen rapidly raise the Q value, to thereby output sharp pulse laserhaving a very high energy value. The method is one of known techniques.

[0019] The solid state laser used in the present invention can outputlaser light as long as a solid crystal, a resonant mirror, and a lightsource for exciting the solid crystal are satisfied, basically.Therefore, maintenance thereof is not laborious unlike the excimerlaser. In other words, the running cost of the solid state laser issignificantly less as compared with the excimer laser, making itpossible to greatly reduce the production cost of a semiconductordevice. A decrease in number of the maintenance leads to an increase ofthe operating rate of the mass-production line, so that the throughputalong the manufacturing steps is improved as a whole. This alsocontributes considerably to the reduction in production cost of thesemiconductor device. Moreover, the solid state laser occupies a smallerarea than the excimer laser does, which is advantageous in designing aproduction line.

[0020] In addition, to perform laser annealing by irradiating the frontside and the back side of an amorphous semiconductor film with laserlight allows obtainment of a crystalline semiconductor film with alarger crystal grain size than in prior art (where the amorphoussemiconductor film is irradiated with laser light only from its frontside). According to the applicant of the present invention, it isconsidered that irradiation of laser light onto the front side and theback side of an amorphous semiconductor film slows down the cycle offusion and solidification of the semiconductor film, and that thecrystal grain size is increased as a result.

[0021] The obtainment of a crystalline semiconductor film with a largecrystal grain size leads to a considerable improvement of theperformance of the semiconductor device. Taking a TFT as an example,enlargement of a crystal grain size allows reduction in number ofcrystal grain boundaries that may be contained in a channel formationregion. That is, it allows fabricating a TFT that has one, preferablyzero, crystal grain boundary in its channel formation region. Since thecrystallinity of each crystal grain is such that it may substantially beregarded as a single crystal, to obtain a mobility (electric fieldeffect mobility) equal to or higher than that of a transistor using asingle crystal semiconductor is also possible.

[0022] Further, carriers cross the crystal grain boundaries extremelyless frequently in the present invention to thereby reduce thefluctuation of ON current values (drain current when a TFT is in ONstate), OFF current values (drain current when a TFT is in OFF state),threshold voltage, of S values, and electric field effect mobility.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In the accompanying drawings:

[0024]FIGS. 1A and 1B are diagrams showing the structure of a laserapparatus;

[0025]FIGS. 2A and 2B are diagrams showing the structure of an opticalsystem of a laser apparatus;

[0026]FIG. 3 is a diagram illustrating a laser annealing method of thepresent invention;

[0027]FIGS. 4A and 4B are diagrams showing the structure of a laserapparatus;

[0028]FIG. 5 is a diagram illustrating a laser annealing method of thepresent invention;

[0029]FIG. 6 is a diagram illustrating a laser annealing method of thepresent invention;

[0030]FIGS. 7A to 7E are diagrams showing a process of manufacturing anactive matrix substrate;

[0031]FIGS. 8A to 8D are diagrams showing a process of manufacturing anactive matrix substrate;

[0032]FIGS. 9A to 9C are diagrams showing a process of manufacturing anactive matrix substrate;

[0033]FIGS. 10A to 10E are diagrams showing a process of manufacturingan active matrix substrate;

[0034]FIGS. 11A to 11E are diagrams showing a process of manufacturingan active matrix substrate;

[0035]FIG. 12 is a diagram showing a pixel structure;

[0036]FIGS. 13A and 13B are diagrams showing the sectional structure ofan active matrix type liquid crystal display device;

[0037]FIG. 14 is a diagram showing the top structure of an active matrixtype liquid crystal display device;

[0038]FIG. 15 is a perspective view showing an active matrix type liquidcrystal display device;

[0039]FIGS. 16A to 16F are diagrams showing examples of an electronicdevice;

[0040]FIGS. 17A to 17D are diagrams showing examples of a projector; and

[0041]FIG. 18 is a diagram illustrating a laser annealing method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Embodiment Mode 1

[0043] An embodiment mode of the present invention will be described.FIG. 1A is a diagram showing the structure of an laser apparatusincluding a laser of the present invention. This laser apparatus has anNd:YAG laser 101, an optical system 201 for linearizing laser light(preferably second harmonic, third harmonic, or fourth harmonic)generated and emitted from an Nd:YAG laser 101, and a stage 102 on whicha light transmittable substrate is fixed. The stage 102 is provided witha heater 103 and a heater controller 104 to heat the substrate up to atemperature of 100 to 450° C. A reflective member 105 is provided on thestage 102, and placed on the reflective member 105 is a substrate 106 onwhich an amorphous semiconductor film is formed.

[0044] If the laser light output from the Nd:YAG laser 101 is modulatedinto any of the second to fourth harmonics, a wavelength modulatorincluding a non-linear element is set right behind the Nd:YAG laser 101.

[0045] Next will be described, with reference to FIG. 1B, how to holdthe substrate 106 in the laser apparatus having the structure as shownin FIG. 1A. The substrate 106 held by the stage 102 is set in a reactionchamber 107, and irradiated with linear laser light generated andemitted from the laser 101 as a source. The inside of the reactionchamber may be decompressed by an exhaust system (not shown), or mayhave an inert gas atmosphere by using a gas system (not shown), so thatthe semiconductor film can be heated up to a temperature of 100 to 450°C. without contaminating the film.

[0046] The stage 102 can be moved along a guide rail 108 within thereaction chamber, making it possible to irradiate the entire surface ofthe substrate with laser light. The laser light enters from a not-shownwindow that is formed from quarts on the top surface of the substrate106. In FIG. 1B, a transfer chamber 109, an intermediate chamber 110,and a loading/unloading chamber 111 are connected to the reactionchamber 107, and these chambers are separated from each other by gatevalves 112, 113.

[0047] A cassette 114 that is capable of holding a plurality ofsubstrates is placed in the loading/unloading chamber 111. Thesubstrates are transported by a transporting robot 115 that is installedin the transfer chamber 109. Reference symbol 106′ denotes a substratein the transportation. With such a structure, successive laser annealingcan be carried out under reduced pressure or in an inert gas atmosphere.

[0048] Next, the structure of the optical system 201 for linearizinglaser light will be described with reference to FIGS. 2A and 2B. FIG. 2Ais a view of the optical system 201 viewed from its side, and FIG. 2B isa view of the optical system 201 viewed from its top.

[0049] The laser light generated and emitted from the laser 101 as asource is split longitudinally by a cylindrical lens array 202. Thesplit laser light is further split laterally by a cylindrical lens array203. That is, ultimately, the laser light is split by the cylindricallens arrays 202, 203 into matrix.

[0050] Then the laser light is condensed once by a cylindrical lens 204.The laser light passes through a cylindrical lens 205 right after thecylindrical lens 204. Thereafter, the laser light is reflected at amirror 206, passes through a cylindrical lens 207, and then reaches anirradiated area 208.

[0051] At this point, the laser light projected onto the irradiated area208 is linear. This means that the sectional shape of the laser lighttransmitted through the cylindrical lens 207 is linear. The linearizedlaser light is homogenized in its width direction (shorter one) by thecylindrical lens array 202, the cylindrical lens 204, and thecylindrical lens 207. On the other hand, the linearized laser light ishomogenized in its length direction (longer one) by the cylindrical lensarray 203 and the cylindrical lens 205.

[0052] A description given next with reference to FIG. 3 is about anarrangement for irradiating the process film formed on the substratefrom its front and back with the laser light. FIG. 3 is a diagramshowing the positional relation between the substrate 106 and thereflective member 105 in FIG. 1A.

[0053] In FIG. 3, reference symbol 301 denotes a light transmittablesubstrate, the front side (the side where a thin film or an element isto be formed) of which has an insulating film 302 and an amorphoussemiconductor film (or a microcrystal semiconductor film) 303 formedthereon. A reflective member 304 for reflecting laser light is arrangedbeneath the light transmittable substrate 301.

[0054] The light transmittable substrate 301 may be a glass substrate, aquartz substrate, a crystallized glass substrate or a plastic substrate.For the insulating film 302, an insulating film containing silicon, suchas a silicon oxide film or a silicon oxide nitride film (SiOxNy) film,may be used. Prospective films for the amorphous semiconductor film 303include an amorphous silicon film, an amorphous silicon germanium film,etc.

[0055] A metal film formed on a surface (where the laser light is to bereflected) of a substrate may be used as the reflective member 304.Alternatively, a substrate formed of a metal element may serve as thereflective member 304. In that case, any material may be used for themetal film. Typically used is a metal film containing any element chosenout of aluminum, silver, tungsten, titanium, and tantalum.

[0056] It is also possible to directly form a metal film as above on theback side of the substrate 301, instead of arranging the reflectivemember 304, so that the laser light is reflected at the metal film. Notethat this structure is possible only when the metal film formed on theback side is not removed during the manufacture of a semiconductordevice.

[0057] The amorphous semiconductor film 303 is then irradiated with thelaser light that has been linearized through the optical system 201(only the cylindrical lens 207 is shown in the drawing) illustrated inFIGS. 2A and 2B.

[0058] At this point, the amorphous semiconductor film 303 is irradiatedwith two beams of laser light, i.e., laser light 305 that passes throughthe cylindrical lens 207 to directly irradiate the film, and laser light306 that is reflected at the reflective member 304 before it irradiatesthe amorphous semiconductor film 303. In this specification, the laserlight used to irradiate the front side of the amorphous semiconductorfilm is called a primary laser light while the laser light used toirradiate the back side thereof is called a secondary laser light.

[0059] The laser light passes through the cylindrical lens 207 to havean angle of incident of 45 to 90° with respect to the front side of thesubstrate during the process of being condensed. For that reason, thesecondary laser light 306 is the light that reaches further to the backside of the amorphous semiconductor film 303 so as to irradiate there.The secondary laser light 306 may be obtained more efficiently byforming an uneven portion on the reflective surface of the reflectivemember 304 to diffuse the laser light.

[0060] In particular, the second harmonic of the YAG laser has afrequency of 532 nm and is within a wavelength range (around 530 nm) inwhich reflection at an amorphous semiconductor film is the least whenthe amorphous semiconductor film is irradiated with the second YAG laserwave. In this wavelength range, in addition, the quantity oftransmittable laser light through the amorphous semiconductor film isenough to efficiently irradiate again the amorphous semiconductor filmfrom its back side using the reflective member. Moreover, the laserenergy of the second harmonic is large, about 1.5 J/pulse at a maximum(in an existing pulse oscillation type YAG laser apparatus). When it islinearized, the length thereof in the longitudinal direction istherefore markedly lengthened to make it possible to irradiate a largearea at once with laser light.

[0061] As described above, according to this embodiment mode, the laserlight generated and emitted from the solid state laser as a source canbe linearized, and the linearized laser light can be split into theprimary laser light and the secondary laser light in the optical systemso as to be used to irradiate the front side of the amorphoussemiconductor film and the back side thereof, respectively.

[0062] Embodiment Mode 2

[0063] A description given here is a different mode for carrying out thepresent invention from Embodiment Mode 1. This embodiment mode shows anexample in which, without using a reflecting member as described inEmbodiment Mode 1, an amorphous semiconductor film is irradiated fromits front and back with laser light split into two strains of laserlight by some constituent of an optical system.

[0064]FIG. 4A is a diagram showing the structure of a laser apparatusincluding a laser of this embodiment mode. The structure is basicallythe same as that of the laser apparatus described in Embodiment Mode 1with FIGS. 1A and 1B. Accordingly, only parts different from the ones inthe precedent mode are given different symbols and are explained.

[0065] This laser apparatus has an Nd:YAG laser 101, an optical system401 for linearizing laser light that is generated and emitted from anNd:YAG laser 101 and splitting into two strains laser light (preferablythird harmonic, or fourth harmonic), and a light transmittable stage 402on which a light transmittable substrate is fixed. A substrate 403 a isset on the stage 402, and an amorphous semiconductor film 403 b isformed on the substrate 403 a.

[0066] If the laser light output from the Nd:YAG laser 101 is modulatedinto either the third harmonic or the fourth harmonic, a wavelengthmodulator including a non-linear element is set right behind the Nd:YAGlaser 101.

[0067] In the case of this embodiment mode, the amorphous semiconductorfilm 403 b is irradiated with laser light that has been transmittedthrough the stage 402, and hence the stage 402 has to be lighttransmittable. It is desirable to suppress as much attenuation aspossible at the stage 402, because the energy of the laser lightirradiated from the stage 402 (a secondary laser light) is expectedlyattenuated when the laser light is transmitted through the substrate.

[0068]FIG. 4B is a diagram illustrating how to hold the substrate 403 ain the laser apparatus shown in FIG. 4A. The explanation thereof isomitted, however, for the arrangement thereof is the same as the oneshown in FIG. 1B except that the light transmittable stage 402 is usedhere.

[0069] Next, the structure of the optical system 401 shown in FIG. 4Awill be described with reference to FIG. 5. FIG. 5 is a view of theoptical system 401 viewed from its side. Laser light generated andemitted from an Nd:YAG laser 501 as a source (the third harmonic or thefourth harmonic) is split longitudinally by a cylindrical lens array502. The split laser light is further split laterally by a cylindricallens array 503. The laser light is thus split by the cylindrical lensarrays 502, 503 into matrix.

[0070] Then the laser light is condensed once by a cylindrical lens 504.The laser light passes through a cylindrical lens 505 right after thecylindrical lens 504. The optical system 401 is the same as the oneshown in FIGS. 2A and 2B up through this point.

[0071] Thereafter, the laser light enters into a half mirror 506 and issplit here into a primary laser light 507 and a secondary laser light508. The primary laser light 507 is reflected at mirrors 509, 510,passes through a cylindrical lens 511, and then reaches the front sideof the amorphous semiconductor film 403 b.

[0072] The secondary laser light 508 split by the half mirror 506 isreflected at mirrors 512, 513, 514, passes through a cylindrical lens515, and then transmits through the substrate 403 a to reach the backside of the amorphous semiconductor film 403 b.

[0073] At this point, the laser light projected onto an irradiated areaon the substrate is linear as in Embodiment Mode 1. The linearized laserlight is homogenized in its width direction (shorter one) by thecylindrical lens array 502, the cylindrical lens 504, and thecylindrical lens 515. On the other hand, the linearized laser light ishomogenized in its length direction (longer one) by the cylindrical lensarray 503, the cylindrical lens 505, and the cylindrical lens 509.

[0074] As described above, according to this embodiment mode, the laserlight generated and emitted from the solid state laser as a source canbe linearized, and the linearized laser light can be split into theprimary laser light and the secondary laser light so as to be used toirradiate the front side of the amorphous semiconductor film and theback side thereof, respectively.

[0075] Embodiment Mode 3

[0076] A description given here is about an embodiment mode differentfrom Embodiment Mode 2. This embodiment mode shows an example in whichlaser light is split into two strains of laser light by some constituentof an optical system, the two laser beams are made into a third harmonicand a fourth harmonic, respectively, and laser annealing of an amorphoussemiconductor film is carried out by irradiating its front with thefourth harmonic while irradiating its back with the third harmonic.

[0077]FIG. 6 is a side view of the optical system of a laser apparatusfor use in this embodiment mode. The laser light generated and emittedfrom an Nd:YAG laser 601 as a source is split by a half mirror 602. Notethat, though not shown, a part of a fundamental wave output from theNd:YAG laser 601 is modulated into a third harmonic having a wavelengthof 355 nm before reaching the half mirror 602.

[0078] First, laser light which has transmitted through the half mirror602 (to serve as a secondary laser light) travels through cylindricallens arrays 603, 604, cylindrical lenses 605, 606, a mirror 607, acylindrical lens 608, and a substrate 609 a to be used to irradiate theback side of an amorphous semiconductor film 609 b.

[0079] The laser light used ultimately to irradiate the back side of anamorphous semiconductor film 609 b is linearized. The process oflinearization is the same as in the explanation of the optical system ofFIGS. 2A and 2B, and hence is not described here.

[0080] Laser light which has been reflected at the half mirror 602 (toserve as a primary laser light) is modulated into a fourth harmonichaving a wavelength of 266 nm by a wavelength modulator 610 thatincludes a non-linear element. Thereafter, the laser light travelsthrough a mirror 611, cylindrical lens arrays 612, 613, cylindricallenses 614, 615, a mirror 616, and a cylindrical lens 617 to be used toirradiate the front side of the amorphous semiconductor film 609 b.

[0081] The laser light used ultimately to irradiate the back side of anamorphous semiconductor film 609 b is linearized. The process oflinearization is the same as in the explanation of the optical system ofFIGS. 2A and 2B, and hence is not described here.

[0082] As described above, this embodiment mode is characterized in thatthe front side of the amorphous semiconductor film is irradiated withthe fourth harmonic with a wavelength of 266 nm while the back side ofthe amorphous semiconductor film is irradiated with the third harmonicwith a wavelength of 355 nm. It is preferable to linearize the sectionalshape of the third harmonic and the fourth harmonic as in thisembodiment mode, for the throughput of the laser annealing is improved.

[0083] When the substrate 609 a is a glass substrate, light with awavelength shorter than 250 nm or so does not transmit through thesubstrate. As for the #1737 substrate with a thickness of 1.1 mm, aproduct of Corning, Ltd., light with a wavelength of about 240 nm is thefirst that can transmit the substrate. The substrate allows about 38% oflight with a wavelength of 300 nm to transmit therethrough, about 85% ifit is 350 nm, and about 90% if it is 400 nm. That is, to use laser lightwith a wavelength of 350 nm or more (preferably with 400 nm or morewavelength) as the secondary laser light is desirable when a glasssubstrate is employed for the substrate 609 a.

[0084] Accordingly, when an Nd:YAG laser is used for a solid state laserand a glass substrate is used for the substrate on which the amorphoussemiconductor film is formed as in this embodiment mode, it is desirableto make the primary laser light that does not transmit the substrateinto the fourth harmonic and to make the secondary laser light thattransmits the substrate into the third harmonic.

[0085] As described above, it is effective to adopt a differentwavelength of the laser light used to irradiate the front side of theamorphous semiconductor film (the primary laser light) from a wavelengthof the laser light used to irradiate the back side of the amorphoussemiconductor film (the secondary laser light), in accordance with thematerial of the substrate or the film quality of the amorphoussemiconductor film.

[0086] Although used in this embodiment mode is split laser light whichhas been generated and emitted from one laser as a source, two lasersthat output laser light of different wavelengths may alternatively beused.

[0087] Embodiment 1

[0088] An embodiment of the present invention is described by usingFIGS. 7A to 9C. A method for manufacturing a pixel TFT and a storagecapacitor of the pixel section, and an n-channel TFT and a p-channel TFTof the driver circuit disposed in the periphery of the pixel section, atthe same time, is described here.

[0089] In FIG. 7A, barium borosilicate glass or aluminoborosilicateglass as typified by Corning #7059 glass and #1737 glass can be used fora substrate 701. Besides these glass substrates, plastic substrates nothaving optical anisotropy such as polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polyethersulfone (PES), etc. can also beused.

[0090] A base film 702 comprising such as a silicon oxide film, asilicon nitride film or a silicon oxynitride film is formed over thesurface of the substrate 701, on which TFT is to be formed, in order toprevent the diffusion of impurities from the substrate 701. For example,a laminate of the silicon oxynitride film 702 a formed from SiH₄, NH₃and N₂O by plasma CVD to a thickness of 10 to 200 nm (preferably, 50 to100 nm) and a hydrogenated silicon oxynitride film 702 b formedsimilarly from SiH₄ and N₂O to a thickness of 50 to 200 nm (preferably,100 to 150 nm), is formed.

[0091] The silicon oxynitride film is formed by using the conventionalparallel plate type plasma-enhanced CVD. The silicon oxynitride film 702a is formed by introducing SiH, at 10 sccm, NH₃ at 100 sccm and N₂O at20 sccm into a reaction chamber under the condition of a substratetemperature of 325° C., a reaction pressure of 40 Pa, a discharge powerdensity of 0.41 W/cm² and a discharge frequency of 60 MHZ. On the otherhand, hydrogenated silicon oxynitride film 702 b is formed byintroducing SiH₄ at 5 sccm, N₂O at 120 sccm and H₂ at 125 sccm into areaction chamber under the condition of the substrate temperature 400°C., a reaction pressure of 20 Pa, a discharge power density of 0.41W/cm² and a discharge frequency of 60 MHZ. These films can be formedsuccessively by only changing the substrate temperature and by switchingthe reactive gases.

[0092] Further, the silicon oxynitride film 702 a is formed so that itsinternal stress is a pulling stress when considering the substrate asthe center. The silicon oxynitride film 702 b is made to have itsinternal stress in the similar direction but it is made to have asmaller stress in the absolute value, compared with that of the siliconoxynitride film 702 a.

[0093] Next, an amorphous semiconductor film 703 having a thickness of25 to 80 nm (preferably, 30 to 60 nm) and an amorphous structure isformed by a known method such as plasma CVD or sputtering. For example,an amorphous silicon film is formed to a thickness of 55 nm by plasmaCVD. Both the base film 702 and the amorphous semiconductor film 703 canbe formed continuously. For example, after the silicon oxynitride film702 a and the hydrogenated silicon oxynitride film 702 b are formedcontinuously by the plasma CVD as described above, the deposition can becarried out continuously by switching the reactive gases from SiH₄, N₂Oand H₂ to SiH₄ and H₂, or SiH₄ alone, without exposing to the atmosphereof the open air. As a result, the contamination of the surface of thehydrogenated silicon oxynitride film 702 b can be prevented, andvariance of the characteristics of the TFT to be fabricated andfluctuation of the threshold voltage can be reduced.

[0094] Island semiconductor layers 704 to 708 are then formed into thefirst shape as shown by dotted line in FIG. 7B, from the semiconductorlayer 703 which has an amorphous structure. FIG. 10A is a top view ofisland semiconductor layers 704 and 705 of this state and FIG. 11Asimilarly shows a top view of an island semiconductor layer 708.

[0095] In FIGS. 10 and 11 the island semiconductor layers are formedinto rectangles of each side at 50 μm or less however it is possible toform the shape of the island semiconductor layers arbitrarily,preferably provided that the minimum distance from its center to theedge is 50 μm or less it may can be any polygon or circular shape.

[0096] Next crystallization process is performed onto such islandsemiconductor layers 704 to 708. It is possible to use any methoddescribed in Embodiment Modes 1 to 3 for the crystallization process,and laser anneal is performed onto the island semiconductor layers 704to 708 by the method of Embodiment Mode 1 in this Embodiment. Islandsemiconductor layers 709 to 713 are thus formed from crystalline siliconfilm as shown by the solid line in FIG. 7B.

[0097] Note that though the present Embodiment shows an example offorming one island semiconductor layer corresponding to one TFT, it ispossible to make a plural numbers of TFTs connected in series functionas one TFT by partitioning one island semiconductor layers into pluralnumbers, in case that the surface area exclusively used by an islandsemiconductor layer is large (in case that one TFT becomes large).

[0098] In this case the film becomes dense as the amorphous silicon filmcrystallizes and it shrinks by about 1 to 15%. A region 714 is formed inthe edge portion of the island semiconductor layer in which strain isgenerated due to the shrinkage. Further, an island semiconductor layercomprising such crystalline silicon film has a pulling stress byconsidering the substrate as its center. FIGS. 10B and 11B respectivelyshows a top view of island semiconductor layers 709, 710 and 713 of thisstate. The regions 704, 705 and 708 shown by dotted line in the samefigures show the size of the island semiconductor layers 704, 705 and708 that existed from the first.

[0099] When a gate electrode of a TFT is formed overlapping the region714 in which such strain is accumulated, it becomes a cause fordegrading the TFT characteristics since there are a number of defectlevels and the crystallinity is no good. OFF current value increases orheat is generated regionally because current is concentrated into thisregion, for instance.

[0100] Accordingly as shown in FIG. 7C, island semiconductor layers 715to 719 of the second shape are formed so as to remove the region 714 inwhich such strain is accumulated. The region 714′ shown by a dotted linein the figure is an area where the region 714 in which strain isaccumulated existed, and the figure shows the condition in which islandsemiconductor layers 715 to 719 of the second shape are formed insidesuch area. The shape of the island semiconductor layers 715 to 719 ofthe second shape may be set arbitrarily. FIG. 10C shows a top view ofthe island semiconductor layers 715 and 714 of this state. Further, FIG.11C shows a top view of the island semiconductor layer 719.

[0101] Thereafter a mask layer 720 is formed from silicon oxide filminto 50 to 100 nm by plasma CVD or sputtering, so as to cover the islandsemiconductor layers 715 to 719. An impurity element which impartsp-type may be added onto the entire surface of the island semiconductorlayers of this state to a concentration from 1×10¹⁶ to 5×10¹⁷ atoms/cm³for the purpose of controlling the threshold voltage of the TFTs (VT).

[0102] The elements of the Group XIII of the Periodic Table such asboron (B), aluminum (Al) or gallium (Ga) are known as the impurityelements for imparting p-type to the semiconductor. Ion implantation orion doping can be adopted as the method of doping these elements, bution doping is suitable for processing a substrate having a large area.This ion doping method uses diborane (B₂H₆) as a source gas and addsboron (B). Addition of such an impurity element is not always necessaryand may be omitted. However, this is the method that can be usedappropriately for keeping the threshold voltage of the n-channel TFT, inparticular, within a prescribed range.

[0103] In order to form an LDD region in the n-channel TFT in the drivercircuit, an impurity element for imparting the n type is selectivelyadded into island semiconductor layers 716 and 718. Resist masks 721 ato 721 e are formed in advance for this purpose. As an impurity elementwhich imparts n-type, phosphorus (P) or arsenic (As) may be used and iondoping using phosphine (PH₃) is used here for adding phosphorus (P).

[0104] The concentration of phosphorus (P) in the formed impurityregions may be within the range of 2×10¹⁶ to 5×10¹⁹ atoms/cm³ as the lowconcentration n-type impurity regions 722 and 723. Through thespecification the concentration of the impurity element which impartsn-type contained in the impurity regions 722 and 723 formed here isdenoted as (n⁻). Further, the impurity region 724 is a semiconductorlayer for forming a storage capacitor of the pixel section andphosphorus (P) is added in this region as well in the sameconcentration. (FIG. 7D)

[0105] A step for activating the added impurity element is performednext. The activation can be performed by heat treatment in a nitrogenatmosphere at 500 to 600° C. for 1 to 4 hours or laser activation.Further, the two may be performed in combination. In case of adoptinglaser activation, KrF excimer laser light (wavelength 248 nm) is used, alinear beam is formed under the condition of oscillation frequency 5 to50 Hz and energy density at 100 to 500 mJ/cm², and the beam is scannedwith the overlap ratio of the linear beam to 80 to 98% to treat theentire surface of the substrate on which island semiconductor layers areformed. Note that there is no item that limits the laser lightirradiation conditions and they may be appropriately determined by theoperator. This process may be performed with the mask layer 720remained, or it may be performed after removal.

[0106] In FIG. 7E, the gate insulating film 725 is formed from aninsulating film containing silicon to a thickness between 40 and 150 nmby using plasma CVD or sputtering. For example, it may be formed from asilicon oxynitride film to 120 nm thickness. Further, the siliconoxynitrode film manufactured by adding O₂ to SiH₄ and N₂O has a reducedfixed electric charge density in the film and therefore is a preferablematerial for this use. Needless to say, the gate insulating film 725 isnot limited to such silicon oxynitride film, and it may use a singlelayer or a laminate structure of other insulating films containingsilicon. In any case, the gate insulating film 725 is formed so as to bea compressing stress by considering the substrate as its center.

[0107] A heat resistant conductive layer is formed as shown in FIG. 7Eto form a gate electrode on the gate insulating film 725. The heatresistant conductive film may comprise a single layer, but may be alaminate structure of plurality of layers such as double layer or triplelayer, if necessary. By using such heat resistant conductive materials,the structure in which the conductive layer (A) 726 comprising aconductive metal nitride film and the conductive layer (B) 727 whichcomprises a metal film are laminated may be formed for example.

[0108] The conductive layer (B) 727 may be formed from an elementselected from tantalum (Ta), titanium (Ti), molybdenum (Mo) and tungsten(W), or an alloy film comprising mainly of these elements or an alloyfilm combining the above elements (typically, a Mo—W alloy film, anMo—Ta alloy film), and the conductive layer (A) 726 may be formed fromtantalum nitride (TaN), tungsten nitride (WN), titanium nitride (TiN),molybdenum nitride (MoN), etc. The conductive layer (A) 726 may adopttungsten silicide, titanium silicide or molybdenum suicide.

[0109] The impurity concentration contained in the conductive layer (B)727 may be preferably reduced for low resistance, specifically theoxygen concentration may be reduced to 30 ppm or below. For example,resistivity of 20 μΩcm or below can be realized with respect to tungsten(W) by setting the oxygen concentration at 30 ppm or below.

[0110] The conductive layer (A) 726 may be formed to 10 to 50 nm(preferably 20 to 30 nm) and the conductive layer (B) 727 may be formedto 200 to 400 nm (preferably 250 to 350 nm). In the case of using W forthe gate electrode, tungsten nitride (WN) is formed to a thickness of 50nm for the conductive layer (A) 726 by sputtering using W as a targetand by introducing an argon (Ar) gas and a nitrogen (N₂) gas, and W isformed to a thickness of 250 nm for the conductive layer (B) 727. Asanother method, W film can be formed by thermal CVD using tungstenhexafluoride (WF₆).

[0111] In any case, it is necessary to devise low resistivity for usingas a gate electrode, and the resistivity of the W film is preferably nothigher than 20 μΩcm. The low resistivity of the W film can beaccomplished by increasing the crystal grain size, but the resistivitybecomes high when the contents of the impurity elements such as oxygenin W are great because crystallization is impeded. Therefore, whensputtering is employed, the W target used has a purity of 99.9999%, andsufficient attention should be paid lest impurities mix from the gaseousphase during the formation of the film. In this way, the resistivity of9 to 20 μΩcm can be achieved.

[0112] On the other hand, in case of using TaN film for the conductivelayer (A) 726 and Ta film for the conductive layer (B) 727, it ispossible to form similarly by sputtering. TaN film is formed by using Taas the target and the mixed gas of Ar and nitrogen for the sputteringgas, and argon (Ar) is used as the sputtering gas to form the Ta film.When a suitable amount of Xe or Kr is added to the sputtering gas, theinternal stress of the resulting films can be mitigated and peel of thefilms can be prevented. The resistivity of the a phase Ta film is about20 μΩcm, and this film can be used for the gate electrode. However, theresistivity of the β phase Ta film is about 180 μΩcm and this film isnot suitable for the gate electrode. The TaN film has a crystalstructure approximate to that of the a phase. Therefore, when the Tafilm is formed on the TaN film, the a phase Ta film can be obtainedeasily.

[0113] Incidentally, though not shown in the figure, it is effective toform a phosphorus (P) doped silicon film to a thickness of about 2 toabout 20 nm under the conductive layer (A) 726. By doing so, theimprovement of adhesiveness and prevention of oxidation of theconductive film formed thereon can be devised and at the same time it ispossible to prevent the alkali metal elements contained in theconductive layer (A) 726 or the conductive layer (B) 727 in a traceamount to diffuse into the gate insulating film 725. In any case, it ispreferable to set the resistivity of the conductive layer (B) 727 withina range between 10 and 50 μΩcm.

[0114] Next, resist masks 728 a to 728 f are formed by photolithographyby using a photo-mask, and the conductive layer (A) 726 and theconductive layer (B) 727 are collectively etched to form gate electrodes729 to 733 and a capacitance wiring 734. These gate electrodes 729 to733 and capacitance wiring 734 comprise a unitary structure of 729 a to733 a comprising the conductive layer (A) and 729 b to 733 b comprisingthe conductive layer (B). (FIG. 8A)

[0115] The relations of the arrangement of the island semiconductorlayers 715 and 716 and gate electrodes 729 and 730 in this state isshown in FIG. 10D. Similarly the relations between the islandsemiconductor layer 719, the gate electrode 733 and the capacitor wiring734 is shown in FIG. 11D. The gate insulating film 725 is omitted fromFIGS. 10D and 11D.

[0116] Though the method for etching the conductive layer (A) and theconductive layer (B) may be appropriately selected by the operator, itis preferable to adopt dry etching using high density plasma forperforming etching at a high speed and with high precision, in case thatthey are formed from a material which is mainly composed of W asdescribed above. Microwave plasma or inductively coupled plasma (ICP)etching apparatus may be used as a means for obtaining high densityplasma.

[0117] For example, in etching of W using an ICP etching apparatus, twokinds of gasses, CF₄ and Cl₂, are introduced into the reaction chamber,the pressure is set at 0.5 to 1.5 Pa (preferably 1 Pa) and highfrequency (13.56 MHz) electric power of 200 to 1000W is applied to theinductive coupling section. At this time, high frequency electric powerof 20 W is applied to the stage on which the substrate is placed,charged to negative electric potential by its self bias, positive ionsare accelerated and anisotropic etching can be performed. By using ICPetching apparatus, etching speed of 2 to 5 nm/second can be obtainedeven with hard metal films such as W, etc. Further, in order to etchwithout leaving residues, it is good perform over-etching by extendingthe etching time by a proportion of 10 to 20%. However, it is necessaryto pay attention to the selective ratio of etching with the base film.For example, since the selective ratio of the silicon oxynitride film(gate insulating film 725) against W film is 2.5 to 3, the surface wherethe silicon oxynitride film is exposed is etched approximately 20 to 50nm and becomes substantially thin through such over etching treatment.

[0118] Thereafter, in order to form LDD region in the n-channel TFT ofthe pixel TFT, a process of adding an impurity element which impartsn-type (n⁻⁻ doping process) is performed. An impurity element whichimparts n-type may be added in a self-aligned manner by ion doping usinggate electrodes 729 to 733 as the mask. The concentration of phosphorus(P) added as the impurity element which imparts n-type is set within aconcentration range between 1×10¹⁶ and 5×10¹⁹ atoms/cm³. In this way,low concentration n-type impurity regions 735 to 739 are formed in theisland semiconductor layers as shown in FIG. 8B.

[0119] Formation of high concentration n-type impurity regions whichfunction as source region or drain region (n⁺ doping process) isperformed next in n-channel TFTs. Resist masks 740 a to 740 d are formedfirst by using a photo-mask, and an impurity element imparting n-type isdoped to form high concentration n-type impurity regions 741 to 746.Phosphorus (P) is used as the impurity element imparting n-type. Iondoping using phosphine (PH₃) is employed so that the concentration fallswithin the range of 1×10²⁰ to 1×10²¹ atoms/cm³ (FIG. 8C).

[0120] High concentration p-type impurity regions 748 and 749 thatfunction as source region or drain region are formed in the islandsemiconductor layers 715 and 717 which form p-channel TFTs. An impurityelement which imparts p-type is added here with the gate electrodes 729and 731 as the mask and high concentration p-type impurity regions areformed in a self-aligning manner. At this time the entire surfaces ofthe island semiconductor films 716, 718 and 719 which form n-channelTFTs are covered by forming resist masks 747 a to 747 c by using a photomask.

[0121] High concentration p-type impurity regions 748 and 749 are formedby ion doping that uses diborane (B₂H₆). The boron (B) concentration inthe regions is 3×10²⁰ to 3×10²¹ atoms/cm³ (FIG. 8D).

[0122] Phosphorus (P) is added to the high concentration p-type impurityregions 748 and 749 in a preceding step, in a concentration of 1×10²⁰ to1×10²¹ atoms/cm³ with respect to the high concentration p-type impurityregions 748 a and 749 a, and in a concentration of 1×10¹⁶ to 5×10¹⁹atoms/cm³ with respect to the high concentration p-type impurity regions748 b and 749 b. However, by setting the concentration of boron (B)added in this step to become 1.5 to 3 times higher, no trouble occurs inthe function as the source and drain regions of the p-channel TFT.

[0123] Thereafter, as shown in FIG. 9A, a protective insulating film 750is formed from above the gate electrode and the gate insulating film.The protective insulating film may comprise a silicon oxide film, asilicon oxynitride film, a silicon nitride film or a laminate filmcomprising the combination of these films. In any case, the protectiveinsulating film 750 is formed of an inorganic insulating material. Theprotective insulating film 750 has a film thickness of 100 to 200 nm.

[0124] When the silicon oxide film is used, tetraethyl orthosilicate(TEOS) and O₂ are mixed, and the film can be formed by plasma CVD with areaction pressure of 40 Pa, a substrate temperature of 300 to 400° C.and plasma is discharged at a high frequency (13.56 MHZ) power densityof 0.5 to 0.8 W/cm². When the silicon oxynitride film is used, the filmmay comprise a silicon oxynitride film formed by plasma CVD from SiH₄,N₂O and NH₃ or a silicon oxynitride film formed from SiH₄ and N₂O. Thefilm deposition condition in this case is the reaction pressure of 20 to200 Pa, the substrate temperature of 300 to 400° C., and the highfrequency (60 MHZ) power density of 0.1 to 1.0 W/cm². The hydrogenatedsilicon oxynitride film formed from SiH₄, N₂O and H₂ may be used, aswell. The silicon nitride film can be formed similarly from SiH₄ and NH₃by plasma CVD. The protective insulating film is formed to be acompressing stress by considering the substrate as the center.

[0125] Thereafter, the step of activating the impurity elementsimparting n-type or p-type added in the respective concentrations isconducted. This step is conducted by a thermal annealing method using afurnace annealing oven. Besides the thermal annealing method, it ispossible to employ a laser annealing method and a rapid thermalannealing method (RTA method). The thermal annealing method is conductedin a nitrogen atmosphere containing oxygen in a concentration of 1 ppmor below, preferably 0.1 ppm or below, at 400 to 700° C., typically 500to 600° C. In this embodiment, the heat-treatment is conducted at 550°C. for 4 hours. When a plastic substrate having a low heat-resistanttemperature is used for the substrate 101, the laser annealing method isemployed (FIG. 9B).

[0126] After the activation step, heat-treatment is further conducted inan atmosphere containing 3 to 100% hydrogen at 300 to 450° C. for 1 to12 hours to hydrogenate the island semiconductor layers. This is theprocess step that terminates the dangling bonds in the islandsemiconductor layers by hydrogen that is thermally excited. Plasmahydrogenation (using hydrogen that is excited by plasma) may be used asanother means for hydrogenation. Further if the thermal resistance ofthe substrate 701 permits, island semiconductor layers may behydrogenated by diffusing hydrogen from the hydrogenated siliconoxynitride film 702 b of the base film and the hydrogenated siliconoxynitride film of the protective insulating film 750, by heat treatmentat 300 to 450° C.

[0127] After the activation and hydrogenation steps are completed, aninterlayer insulating film 751 made of an organic insulating material isformed to a mean thickness of 1.0 to 2.0 μm. As the organic resinmaterials, polyimide, acrylic, polyamide, polyimidamide, BCB(benzocyclobutene), and so forth can be used. For example, whenpolyimide of the type, that is thermally polymerized after being appliedto the substrate, is used, the material is baked at 300° C. in a cleanoven. When acrylic is used, a two-component type is used. After the mainagent and the curing agent are mixed, the mixture is applied to theentire surface of the substrate by using a spinner. Preparatory heatingis then conducted by using a hot plate at 80° C. for 60 seconds, andbaking is then made in the clean oven at 250° C. for 60 minutes.

[0128] By forming the interlayer insulating film from an organicinsulating material, its surface can be planarized satisfactorily. Theorganic resin materials have generally a low dielectric constant, andthe parasitic capacitance can be reduced. However, since they arehygroscopic, they are not suitable for the protective film. Therefore,the organic insulating material must be used in combination with thesilicon oxide film, the silicon oxynitride film or the silicon nitridefilm formed as the protective insulating film 750 as in this embodiment.

[0129] Thereafter, a resist mask having a predetermined pattern isformed by using a photo-mask. Contact holes reaching the source or drainregions of the respective island semiconductor layers are formed. Thecontact holes are formed by dry etching. In this case, a mixed gas ofCF₄, O₂ and He is used as the etching gas. The interlayer insulatingfilm 751 formed of the organic insulating material is first etched.Then, the etching gas is switched to CF₄ and O₂, and the protectiveinsulating film 750 is etched. To improve the selective ratio with theisland semiconductor layers, the etching gas is switched further to CHF₃and the gate insulating film 725 is etched. In this way, the contactholes can be formed satisfactorily.

[0130] A conductive metal film is then formed by sputtering or vacuumvapor deposition, a resist mask is formed by a photo mask and sourcewirings 752 to 756 and drain wirings 757 to 761 are formed by etching.The drain wiring 762 denotes a drain wiring of the adjoining pixel.Here, the drain wiring 761 also functions as the pixel electrode. Thoughnot shown in the figure, this electrode is formed from Ti film to athickness between 50 to 150 nm, contact is formed with the semiconductorfilm which forms a source or drain region in the island semiconductorlayer, and aluminum (Al) is formed to a thickness from 300 to 400 nm onthe Ti film, thereby forming a wiring.

[0131]FIG. 10E shows a top view of island semiconductor layers 715 and716, gate electrodes 729 and 730, source wirings 752 and 753 and drainwirings 757 and 758 in this state. Source wirings 752 and 753 areconnected to the island semiconductor layers 715 and 716 through contactholes disposed in the interlayer insulating film (not shown) and theprotective insulating film at reference numerals 830 and 833. Further,drain wirings 757 and 758 are connected to the island semiconductorlayers 715 and 716 in 831 and 832.

[0132] Similarly FIG. 11E shows a top view of the island semiconductorlayer 719, the gate electrode 733, the capacitor wiring 734, the sourcewiring 756 and the drain wiring 761 and the source wiring 756 isconnected to the island semiconductor layers 719 in the contact portion834, and the drain wiring 761, in the contact portion 835.

[0133] In any case, TFTs are formed by forming island semiconductorlayers that have the second shape by removing the areas where strainremains in an area inside of the island semiconductor layers having thefirst shape.

[0134] When the hydrogenation treatment is conducted under this state,favorable results can be obtained for the improvement of TFTperformance. For example, the heat-treatment may be conducted preferablyat 300 to 450° C. for 1 to 12 hours in an atmosphere containing 3 to100% of hydrogen. A similar effect can be obtained by using the plasmahydrogenation method. Such a heat-treatment can diffuse hydrogenexisting in the protective insulating film 750 and the base film 702into the island semiconductor films 715 to 719 and can hydrogenate thesefilms. In any case, the defect density in the island semiconductorlayers 715 to 719 is lowered preferably to 10¹⁶/cm³ or below, and forthis purpose, hydrogen may be added in an amount of about 5×10¹⁸ to5×10¹⁹ atoms/cm³. (FIG. 9C)

[0135] Thus a substrate having the TFTs of the driving circuit and thepixel TFTs of the pixel portion over the same substrate can becompleted. The first p-channel TFT 800, the first n-channel TFT 801, thesecond p-channel TFT 802 and the second n-channel TFT 803 are formed inthe driving circuit. The pixel TFT 804 and the storage capacitance 805are formed in the pixel portion. In this specification, such a substratewill be referred to as an “active matrix substrate” for conveniencesake.

[0136] The first p-channel TFT 800 in the driving circuit has a singledrain structure that comprises in the island semiconductor film 715: thechannel formation region 806; and the source regions 807 a and 807 b andthe drain regions 808 a and 808 b each comprising the high concentrationp-type impurity region.

[0137] In the island semiconductor film 716 of the first n-channel TFT801, there are formed: the channel formation region 809; the LDD region810 that overlaps the gate electrode 730; the source region 812; and thedrain region 811. In the LDD region, the length of this LDD region whichoverlaps the gate electrode 730 in the direction of the channel lengthis 0.5 to 3.0 μm, preferably 1.0 to 2.0 μm. As the length of the LDDregion in the n-channel TFT is determined in this way, a high electricfield occurring in the proximity of the drain region can be mitigated,and the occurrence of hot carriers and degradation of the TFT can beprevented.

[0138] The second p-channel TFT 802 of the driver circuit has the singledrain structure similarly in which the channel formation region 813, thesource regions 814 a and 814 b and the drain regions 815 a and 815 bcomprising the high concentration p-type impurity region are formed inthe island semiconductor film 717.

[0139] A channel formation region 816, LDD regions 817 and 818 whichpartially overlap the gate electrode 732, a source region 820 and adrain region 819 are formed in the island semiconductor film 718 of thesecond n-channel TFT 803. The length of the LDD regions that overlap thegate electrode 732 is also set at between 0.5 and 3.0 μm, preferably 1.0to 2.0 μm. Further, the length of the LDD regions that do not overlapthe gate electrodes in the channel length direction is 0.5 to 4.0 μm,preferably 1.0 to 2.0 μm.

[0140] The channel forming regions 821 and 822, LDD regions 823 to 825,source or drain regions 826 to 828 are formed in the islandsemiconductor film 719 of the pixel TFT 804. The length of the LDDregion in the direction of the channel length is 0.5 to 4.0 μm,preferably 1.5 to 2.5 μm. The storage capacitance 805 is formed from thecapacitor wiring 734, the insulating film comprising the same materialas the gate insulating film and the semiconductor layer 829 that isconnected to the drain region 828 of the pixel TFT 804. In FIG. 9C, thepixel TFT 804 is a double gate structure. However, it may have a singlegate structure or a multi-gate structure having a plurality of gateelectrodes.

[0141]FIG. 12 is a top view showing almost one pixel of the pixelportion. The cross section A-A′ in the drawing corresponds to thesectional view of the pixel portion shown in FIG. 9C. The gate electrode733 of the pixel TFT 804 crosses the island semiconductor layer 719below it through a gate insulating film, not shown in the drawing. Thesource region, the drain region and the LDD region are formed in theisland semiconductor layer, though they are not shown in the drawing.Reference numeral 834 denotes a contact portion between the sourcewiring 756 and the source region 826. Reference numeral 835 denotes acontact portion between the drain wiring 761 and the drain region 828. Astorage capacitance 805 is formed by the overlapping region of thesemiconductor layer 829 that extends from the drain region 828 of thepixel TFT 804 and a capacitance wiring 734 through the gate insulatingfilm.

[0142] An active matrix substrate is completed as described above. Theactive matrix substrate manufactured in accordance with the presentEmbodiment arranges TFTs of appropriate structures corresponding to thespecifications of the pixel section and the driver circuit. By doing soit enables to improve operation performance and the reliability of theelectro-optical device which uses this active matrix substrate.

[0143] Note that in this Embodiment the drain wiring 761 of the pixelTFT 804 is used as it is to the pixel electrode and has a structurecorresponding to a reflection type liquid crystal display device.However, the present invention can correspond to a transmission typeliquid crystal display device by forming a pixel electrode comprising atransparent conductive film which is electrically connected to the drainwiring 761.

[0144] Further, the present Embodiment is an example of manufacturingprocess of a semiconductor device using the present invention is notnecessarily limited to the material and the numerical value range shownin this Embodiment. Further, the arrangement of the LDD regions, etc.,may appropriately determined by the operator.

[0145] Embodiment 2

[0146] The example shown in Embodiment 1 is crystallization of anamorphous semiconductor film by using the methods described inEmbodiment Modes 1 to 3 to perform laser annealing on the film. In theexample, the laser annealing may be performed instead on a semiconductorfilm that has been crystallized to a certain degree but not thoroughly.

[0147] That is, the laser annealing in accordance with the presentinvention is also effective in the case where a crystallinesemiconductor film that has been crystallized by furnace annealing isfurther projected to laser annealing to enhance its crystallinity.

[0148] To be specific, the laser annealing method of Embodiment Modes 1to 3 may be used in the laser irradiation step described in JapanesePatent Application Laid-open No. Hei 7-321339, Japanese PatentApplication Laid-open No. Hei 7-131034, and some other applications.

[0149] After the present invention is applied to the laser irradiationstep of the above publications, a TFT using the crystallinesemiconductor film formed through that step may be formed. In otherwords, this embodiment can be combined with Embodiment 1.

[0150] Embodiment 3

[0151] This embodiment gives a description of a process of manufacturingan active matrix type liquid crystal display device using an activematrix substrate that is fabricated in accordance with Embodiments 1 and2. First, as shown in FIG. 13A, spacers 901 a to 901 f are formed from aresin material by patterning on an active matrix substrate that is in astate illustrated in FIG. 9C. Alternatively, a known spherical silica orthe like may be dispersed and used as the spacer.

[0152] In this embodiment, as the spacers 901 a to 901 f made of a resinmaterial, NN 700 produced by JSR is applied by a spinner and is thenformed into a given pattern through exposure and development treatment.Further, it is heated in a clean oven or the like at a temperature of150 to 200° C. to cure. The thus formed spacers may vary in shapedepending on exposure conditions and development treatment conditions. Apreferable shape for the spacers is a column with flat top, because itensures the mechanical strength as a liquid crystal display panel whenthe active matrix substrate is bonded to an opposite substrate.

[0153] There is no particular limitation on the shape of the spacers andthey may take a conical shape, a pyramidal shape, etc. When a conicalshape is adopted, for example, specific dimensions of the spacers willbe as follows: a height H of 1.2 to 5 μm, a mean radius L1 of 5 to 7 μm,and the ratio between the mean radius L1 and a radius L2 of 1 to 1.5,with a taper angle of ±15° or less on their sides.

[0154] Any arrangement may be taken for the spacers 901 a to 901 f. Apreferred arrangement is as shown in FIG. 13A, in which the spacers areformed to overlap and cover the contact portion 835 of the drain wiring761 (pixel electrode) in the pixel portion. Otherwise, the levelness islost at the contact portion 835 to fail to orientate liquid crystalthere properly. By filling the contact portion 835 with the resin forthe spacer, discrimination or the like can be prevented.

[0155] An orientation film 902 is then formed. Usually, polyimide resinis used for an orientation film of a liquid crystal display element.After forming the orientation film, rubbing treatment is performed sothat liquid crystal molecules are orientated with a certain pretiltangle. It is preferable that a region that has not received the rubbingtreatment extends equal to or less than 2 μm in the rubbing directionfrom the ends of the spacers 901 a to 901 f provided in the pixelportion. In rubbing treatment, static electricity generated often causestrouble. If the spacers 901 a to 901 f are formed to the extent tocover, at least, the source wiring and the drain wiring on the TFT ofthe driver circuit, they not only serve their original role as a spacerbut also protect the TFT from static electricity in the rubbing process.

[0156] A light shielding film 904, an opposite electrode 905 made of atransparent conductive film, and an orientation film 906 are formed onan opposite substrate 903. As the light shielding film 904, a Ti, Cr, orAl film is formed to a thickness of 150 to 300 nm. The oppositesubstrate is then bonded, with a sealing material 907, to the activematrix substrate that has the pixel portion and the driver circuitformed thereon. A filler 908 is mixed in the sealing material 907, andthe filler 908 together with the spacers 901 a to 901 f bonds theopposite substrate and the active matrix substrate with a uniform gaptherebetween.

[0157] Then a liquid crystal material 909 is injected between thesubstrates, which are sealed completely with an end-sealing material(not shown). A known liquid crystal material may be used as the liquidcrystal material 909. For instance, a material that may be used otherthan a TN liquid crystal is a thresholdless antiferroelectric mixedliquid crystal exhibiting an electro-optical response with whichtransmittance varies continuously with respect to the electric field.Some thresholdless antiferroelectric mixed liquid crystal show anelectro-optical response that forms a shape of letter V when graphed.For details thereof, see “Characteristics and Driving Scheme ofPolymer-stabilized Monostable FLCD Exhibiting Fast Response Time andHigh Contrast Ratio with Gray-scale Capability”, H. Furue et al., SID,1998, “A Full-color Thresholdless Antiferroelectric LCD Exhibiting WideViewing Angle with Fast Response Time”. T. Yoshida et al., 841, SID '97DIGEST, 1997, “Thresholdless Antiferroelectricity in Liquid Crystals andIts Application to Displays, S. Inui et al., 671-673, J. Mater. Chem. 6(4), 1996, and U.S. Pat. No. 5,594,569.

[0158] The active matrix type liquid crystal display device shown inFIG. 13B is thus completed. Although the spacers 901 a to 901 e areformed separately on at least the source wiring and the drain wiring onthe TFT of the driver circuit in FIGS. 13A and 13B, the spacers mayinstead be formed to cover the entire surface of the driver circuit.

[0159]FIG. 14 is a top view of an active matrix substrate, showing thepositional relation of a pixel portion and a driver circuit portion to aspacer and a sealing material. A scanning signal driver circuit 1401 andan image signal driver circuit 1402 are provided as driver circuits inthe periphery of a pixel portion 1400. A signal processing circuit 1403such as a CPU and a memory may or may not be added thereto.

[0160] These driver circuits are connected to external input/outputterminal 1410 via a connecting wiring 1411. In the pixel portion 1400, agate wiring group 1404 extending from the scanning signal driver circuit1401 and a source wiring group 1405 extending from the image signaldriver circuit 1402 intersect like a matrix to form pixels. Each of thepixels is provided with a pixel TFT 804 and a capacitor storage 805.

[0161] The spacer 1406 provided in the pixel portion corresponds to thespacer 901 f, and may be provided for every pixel. Alternatively, onespacer may be provided for every several pixels or for every severaltens pixels arranged in matrix. That is, the ratio of the spacers to thetotal of the pixels is appropriately 20 to 100%. Spacers 1407 to 1409provided in the driver circuit portion may cover the entire surfacethereof, or may be separated into plural pieces to coincide with theposition of the source wiring and the drain wiring of each TFT as shownin FIGS. 13A and 13B.

[0162] The sealing material 907 is formed outside the pixel portion1400, the scanning signal control circuit 1401, the image signal controlcircuit 1402, and other signal processing circuit 1403, which are all ona substrate 701, and inside the external input/output terminal 1410.

[0163] The structure of such an active matrix type liquid crystaldisplay is described with reference to a perspective view of FIG. 15. InFIG. 15, the active matrix substrate is comprised of the pixel portion1400, the scanning signal driver circuit 1401, the image signal drivercircuit 1402, and other signal processing circuit 1403 which are formedon the glass substrate 701.

[0164] The pixel portion 1400 is provided with the pixel TFT 804 and thecapacitor storage 805, and the driver circuits provided in the peripheryof the pixel portion are constructed based on a CMOS circuit. Thescanning signal driver circuit 1401 and the image signal driver circuit1402 are connected to the pixel TFT 804 through a gate wiring 733 and asource wiring 756, respectively. A flexible printed circuit 1413 isconnected to the external input/output terminal 1410 with the intentionof using it to input an image signal or the like. The flexible printedcircuit (FPC) 1413 is fixed with a reinforced resin 1412 with anenhanced adhesion strength. The FPC is connected to each driver circuitvia the connecting wiring 1411. Though not shown in the drawing, anopposite substrate 903 is provided with a light shielding film and atransparent electrode.

[0165] The liquid crystal display device having the structure as suchcan be fabricated using an active matrix substrate shown in Embodiments1 and 2. Employing an active matrix substrate shown in FIG. 9C, forinstance, a reflection type liquid crystal display device is obtained,while a transmission type liquid crystal display device is obtained whenemploying an active matrix substrate that uses a transparent conductivefilm for a pixel electrode as shown in Embodiment 1.

[0166] Embodiment 4

[0167] Although Embodiments 1 to 3 show examples where the presentinvention is applied to a liquid crystal display device, the inventionis applicable to any semiconductor device as long as it uses a TFT.

[0168] Specifically, the present invention can be implemented in laserannealing step of a semiconductor film in manufacturing an active matrixtype EL (electroluminescence) display device or an active matrix type EC(electrochromics) display device. In that case, any of the structures ofEmbodiment Modes 1 to 3 may be employed.

[0169] The present invention is an invention pertaining to the laserannealing step out of a manufacturing process of a TFT, and knownprocedures may be applied to the rest of the steps of the manufacturingprocess. Therefore, the present invention is applied to known techniqueswhen manufacturing an active matrix type EL display device or an activematrix type EC display device. To fabricate these display devicesreferring to the manufacturing process illustrated in FIGS. 7A to 9C isalso possible, of course.

[0170] Embodiment 5

[0171] The present invention can be embodied for an electronic device(also called electronic equipment) having an electro-optical device suchas an active matrix type liquid crystal display device or an activematrix type EL as its display. As the electronic device, a personalcomputer, a digital camera, a video camera, a portable informationterminal (such as a mobile computer, a cellular phone, and an electronicbook) a navigation system, etc. can be named.

[0172]FIG. 16A shows a personal computer that is comprised of a mainbody 2001 provided with a micro processor, a memory, etc., an imageinput unit 2002, a display unit 2003, and a keyboard 2004. The presentinvention can be implemented in fabricating the display unit 2003 andother signal processing circuits.

[0173]FIG. 16B shows a video camera that is comprised of a main body2101, a display unit 2102, an audio input unit 2103, operation switches2104, a battery 2105, and an image receiving unit 2106. The presentinvention can be implemented in fabricating the display unit 2102 andother driver circuits.

[0174]FIG. 16C shows a goggle type display that is comprised of a mainbody 2201, display units 2202, and arm portions 2203. The presentinvention can be implemented in fabricating the display units 2202 andother not-shown driver circuits.

[0175]FIG. 16D shows an electronic game machine that is comprised of amain body 2301 loaded with an electric circuit 2308 such as a CPU andwith a recording medium 2304, a controller 2305, a display unit 2303,and a display unit 2302 incorporated in the main body 2301. The displayunit 2303 and the display unit 2302 incorporated in the main body 2301may display the same information. Alternatively, the former may serve asa main display unit while the latter serve as a sub-display unit todisplay information of the recording medium 2304 or the operation statusof the machine. The latter may instead serve as an operating panel byadding thereto the touch sensor function. The main body 2301, thecontroller 2305 and the display unit 2303 transmit signals to oneanother through wired communication, or through wireless communicationor optical communication by providing sensor units 2306, 2307. Thepresent invention can be implemented in fabricating the display units2302, 2303. A conventional CRT display may be used as the display unit2303.

[0176]FIG. 16E shows a player which uses a recording medium in which aprogram is stored (hereinafter referred to as a recording medium) andwhich is comprised of a main body 2401, a display unit 2402, speakerunits 2403, a recording medium 2404, and operation switches 2405. A DVD(Digital Versatile Disc), a compact disc (CD) or the like is used as therecording medium to enable the player to reproduce a music program,display an image, play a video game (or a television game), or displayinformation obtained through the Internet. The present invention can beimplemented in fabricating the display unit 2402 and other drivercircuits.

[0177]FIG. 16F shows a digital camera that is comprised of a main body2501, a display unit 2502, an eye-piece portion 2503, operation switches2504, and an image receiving unit (not shown). The present invention canbe implemented in fabricating the display unit 2502 and other drivercircuits.

[0178]FIG. 17A shows a front type projector that is comprised of a lightsource optical system and display device 2601, and a screen 2602. Thepresent invention can be implemented in fabricating the display deviceand other driver circuits. FIG. 17B shows a rear type projector that iscomprised of a main body 2701, a light source optical system and displaydevice 2702, a mirror 2703, and a screen 2704. The present invention canbe implemented in fabricating the display device and other drivercircuits.

[0179] Illustrated in FIG. 17C is an example of the structure of thelight source optical system and display devices 2601, 2702 that areshown in FIGS. 17A and 17B, respectively. Each of the light sourceoptical system and display devices 2601, 2702 is comprised of a lightsource optical system 2801, mirrors 2802, 2804 to 2806, dichroic mirrors2803, a beam splitter 2807, liquid crystal display devices 2808, phasedifference plates 2809, and a projection optical system 2810. Theprojection optical system 2810 is made up of a plurality of opticallenses.

[0180]FIG. 17C shows a three panel type where three liquid crystaldisplay devices 2808 are used. However, the light source optical systemand display devices are not limited to this type and may be composed ofa single panel type optical system. A light path indicated by the arrowin FIG. 17C may suitably be provided with an optical lens, a film havinga polarizing function, a film for adjusting the phase, an IR film, etc.

[0181] Illustrated in FIG. 17D is an example of the structure of thelight source optical system 2801 that is shown in FIG. 17C. In thisembodiment, the light source optical system 2801 is comprised of areflector 2811, a light source 2812, lens arrays 2813, 2814, apolarization converting element 2815, and a condenser lens 2816. Notethat the light source optical system shown in FIG. 17D is an example andthe system 2801 is not limited to the illustrated structure.

[0182] Although not shown in here, the present invention may beimplemented in manufacturing a navigation system, a reading circuit foran image sensor, etc., in addition to those applications illustrated inthe above. The application range of the present invention is thus sowide that the invention can be implemented in manufacturing electronicdevices of any field.

[0183] Embodiment 6

[0184] In contrast to Embodiment 1 where the methods of Embodiment Modes1 to 3 are used after patterning, this embodiment shows an example withreference to FIG. 18 in which irradiation with laser light is carriedout using the method of Embodiment Mode 1 before the patterning.

[0185] First, a state shown in FIG. 7A is obtained in accordance withEmbodiment 1.

[0186] A step of crystallizing the semiconductor film is then conducted.A description will be given below on the crystallization step employedin this embodiment, i.e., irradiating the front side and the back sideof the semiconductor film with laser light, which is illustrated in FIG.18.

[0187] In FIG. 18, reference symbol 1801 denotes a light transmittablesubstrate with an insulating film 1802 and an amorphous semiconductorfilm (or a microcrystal semiconductor film) 1803 formed on its frontside. A reflective member 1804 for reflecting laser light is arrangedbeneath the light transmittable substrate 1801.

[0188] The light transmittable substrate 1801 may be a glass substrate,a quartz substrate, a crystallized glass substrate or a plasticsubstrate. The light transmittable substrate 1801 by itself can adjustthe effective energy intensity of a secondary laser light. For theinsulating film 1802, an insulating film containing silicon, such as asilicon oxide film or a silicon oxide nitride film (SiOxNy) film, may beused. The adjustment of the effective energy intensity of the secondarylaser light may be made by the insulating film 1802 instead.

[0189] In the structure of FIG. 18, the secondary laser light is a laserlight that passed through the amorphous semiconductor film 1803 once andthen reflected at the reflective member 1804. Accordingly, it is alsopossible to adjust the effective energy intensity of the secondary laserlight by the amorphous semiconductor film 1803. Examples of theamorphous semiconductor film 1803 include a compound semiconductor filmsuch as an amorphous silicon germanium film, other than an amorphoussilicon film.

[0190] A metal film formed on a surface (where the laser light is to bereflected) of a substrate may be used as the reflective member 1804.Alternatively, a substrate formed of an metal element may serve as thereflective member 1804. In that case, any material may be used for themetal film. Typically used is a metal film containing any element chosenout of silicon (Si), aluminum (Al), silver (Ag), tungsten (W), titanium(Ti), and tantalum (Ta). For example, titanium nitride or tantalumnitride (TaN) may be used.

[0191] The reflective member 1804 may be provided in contact with thelight transmittable substrate 1801, or spaced apart therefrom. It isalso possible to directly form a metal film as above on the back side(opposite side of the front side) of the substrate 1801, instead ofarranging the reflective member 1804, so that the laser light isreflected at the metal film. In either way, the effective energyintensity of the secondary laser light can be adjusted by changing thereflectance of the reflective member 1804. If the reflective member 1804is placed apart from the light transmittable substrate 1801, it is alsopossible to adjust the effective energy intensity of the secondary laserlight by gas charged in a gap between the reflective member and thesubstrate.

[0192] The amorphous semiconductor film 1803 is then irradiated with thelaser light that has been linearized through the optical system 201(only the cylindrical lens 207 is shown in the drawing) illustrated inFIGS. 2A and 2B. The irradiation with the linearized laser light is madeby scanning the laser light.

[0193] The important thing, in any case, is that the effective energyintensity ratio (I₀′/I₀) between a primary laser light 1805, whichpasses through the cylindrical lens 207 to be used to irradiate thefront side of the amorphous semiconductor film 1803, and a secondarylaser light 1806, which passes through the amorphous semiconductor film1803 and is reflected once at the reflective member 1804 to be used toirradiated the back side of the amorphous semiconductor film 1803,satisfies the relation of 0<I₀′I₀<1, or 1<I₀′/I₀. To achieve this, thereflectance of the reflective member 1804 to the laser light ispreferably 20 to 80%. At this point, some of the measures forattenuating the effective energy intensity of the secondary laser light,which have been mentioned above in this embodiment, may be combined toobtain the desired intensity ratio.

[0194] The laser light passes through the cylindrical lens 207 to havean angle of incident of 45 to 90° with respect to the front side of thesubstrate during the process of being condensed. For that reason, thesecondary laser light 1806 reaches further to the back side of theamorphous semiconductor film 1803 so as to irradiate there. Thesecondary laser light 1806 may be obtained more efficiently by formingan uneven portion on the reflective surface of the reflective member1804 to diffuse the laser light.

[0195] An appropriate laser light is the one with its wavelength setwithin a wavelength range (around 530 nm) in which the lighttransmission component and the light absorption component with respectto the amorphous semiconductor film 1803 are sufficient. In thisembodiment, the crystallization is made by the second harmonic(wavelength, 532 nm) of a YAG laser.

[0196] Using the second harmonic, a part of the irradiated lighttransmits through the amorphous semiconductor film and is reflected bythe reflective member so that the back side of the amorphoussemiconductor film is irradiated. Therefore, the secondary laser light1806 can be obtained efficiently.

[0197] The obtained semiconductor film is next patterned to gain anisland-like semiconductor film.

[0198] The rest of the steps are carried out in accordance withEmbodiment 1 to obtain an active matrix substrate.

[0199] This embodiment may also be combined with Embodiment 2. IfEmbodiment 3 is used with this embodiment, then an active matrix typeliquid crystal display device is obtained. Moreover, this embodiment maybe applied to the semiconductor devices shown in Embodiments 4 and 5.

[0200] According to the present invention, improvement of the throughputfrom the laser annealing that uses a conventional excimer laser can beachieved by employing a solid state laser that is easy to maintain, aswell as the throughput is improved by linearizing the laser light inlaser annealing. This leads to reduction in production cost of a TFT anda semiconductor device formed from the TFT, such as a liquid crystaldisplay device.

[0201] Moreover, to conduct laser annealing by irradiating both thefront side and the back side of the amorphous semiconductor film withlaser light makes it possible to obtain a crystalline semiconductor filmwith a larger crystal grain size as compared to prior art (where onlythe front side of the amorphous semiconductor film is irradiated withlaser light). The obtainment of the crystalline semiconductor film witha larger crystal grain size further can lead to a great improvement ofthe ability of a semiconductor device.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising the steps of: forming a semiconductor film over a substrate;crystallizing the semiconductor film by irradiation of the secondharmonic of a YVO₄ laser; and patterning the crystallized semiconductorfilm to form a semiconductor island.
 2. A method according to claim 1,wherein the semiconductor film is an amorphous semiconductor film.
 3. Amethod according to claim 1, wherein the semiconductor film is a microcrystal semiconductor film.
 4. A method of manufacturing a semiconductordevice comprising the steps of: forming a semiconductor film over asubstrate; crystallizing the semiconductor film by irradiation of thesecond harmonic of a YVO₄ laser having a linear shape; and patterningthe crystallized semiconductor film to form a semiconductor island.
 5. Amethod according to claim 4, wherein the semiconductor film is anamorphous semiconductor film.
 6. A method according to claim 4, whereinthe semiconductor film is a micro crystal semiconductor film.
 7. Amethod of manufacturing a semiconductor device comprising the steps of:forming a semiconductor film over a substrate; patterning thesemiconductor film to form a semiconductor island; and crystallizing thesemiconductor island by irradiation of the second harmonic of a YVO₄laser.
 8. A method according to claim 7, wherein the semiconductor filmis an amorphous semiconductor film.
 9. A method according to claim 7,wherein the semiconductor film is a micro crystal semiconductor film.10. A method of manufacturing a semiconductor device comprising thesteps of: forming a semiconductor film over a substrate; patterning thesemiconductor film to form a semiconductor island; and crystallizing thesemiconductor island by irradiation of the second harmonic of a YVO₄laser having a linear shape.
 11. A method according to claim 10, whereinthe semiconductor film is an amorphous semiconductor film.
 12. A methodaccording to claim 10, wherein the semiconductor film is a micro crystalsemiconductor film.
 13. A method of manufacturing a semiconductor devicecomprising the steps of: forming a semiconductor film over a substrate;crystallizing the semiconductor film by irradiation of the secondharmonic of a YVO₄ laser; and patterning the crystallized semiconductorfilm to form a semiconductor island, wherein the second harmonic of theYVO₄ laser has a shape at an irradiation surface which has aspect ratioof 10 or more.
 14. A method according to claim 13, wherein thesemiconductor film is an amorphous semiconductor film.
 15. A methodaccording to claim 13, wherein the semiconductor film is a micro crystalsemiconductor film.
 16. A method for manufacturing a semiconductordevice comprising the steps of: forming an insulating film over asubstrate; forming a semiconductor film on the insulating film;crystallizing the semiconductor film by irradiation of the secondharmonic of a YVO₄ laser; and patterning the crystallized semiconductorfilm to form a semiconductor island, wherein the insulating filmcomprises at least one material selected from the group consisting ofsilicon oxide, silicon oxynitride and silicon nitride.
 17. A methodaccording to claim 16, wherein the semiconductor film is an amorphoussemiconductor film.
 18. A method according to claim 16, wherein thesemiconductor film is a micro crystal semiconductor film.